This commit introduces several different things, in particular:
- check type arguments in expressions
- new TypeArgumentList node to deal with diagnostic source
- ConeDiagnostic was moved to fir:cones
- ConeIntermediateDiagnostic to use in inference (?) without reporting
- detailed diagnostics on error type
In particular, this commit includes:
* Attempt to abstract access to FirSourceElement via FirModifier
* Add more visit functions to DeclarationCheckersDiagnosticComponent
* Add messages+factories for 4 modifier-related errors and warnings
* Introduce FirModifierChecker